LibreOffice is actually reducing their dependence on Java. NeoOffice (AFAIK,) is using OpenOffice as their based code. So it makes sense that Libre would be working the best. 
The only things I can think of that would still cause Libre to be slow on the G4 and Intel is the GTK GUI, and core parts still using Java. As for why the G5 is doing better than the C2D, who knows? Maybe the kind of batch work you're doing is just performed faster on the G5.
The only things I can think of that would still cause Libre to be slow on the G4 and Intel is the GTK GUI, and core parts still using Java. As for why the G5 is doing better than the C2D, who knows? Maybe the kind of batch work you're doing is just performed faster on the G5.